1. Field of the Invention
The present invention relates to an air dryer, and more specifically to an air dryer with rotating desiccant.
2. Description of Related Art
The pneumatic braking system of a large, heavy-duty vehicle typically includes an air compressor, a governor for controlling the operating cycle of the air compressor, an air dryer and a reservoir for storing pressurized air for delivery to the brakes. The air compressor operates successively in a loading (compressing) mode and an unloading (non-compressing) mode.
When the pressure in the air reservoir falls below a predetermined minimum pressure, typically about 100 psig, the governor causes the air compressor to operate in the loading mode to compress air for storage in the reservoir. Before the air is stored in the reservoir, it passes through an air dryer that removes moisture and contaminants from the air. When the pressure in the reservoir reaches a desired level, typically about 120 psig, the governor causes the air compressor to operate in the unloading mode and a purge valve in the air dryer opens to the atmosphere.
One type of conventional air dryer includes a removable cartridge with desiccant that dries the compressed air as it flows through the cartridge during the loading mode. During the unloading mode, the governor causes the purge valve in the air dryer to open the inlet of the cartridge to exhaust to atmosphere, the air flow direction is reversed and previously dried compressed air is sent through the cartridge to regenerate the desiccant by removing moisture and contaminants from it. This type of air dryer cannot continuously dry air because the direction of air flow must be reversed in a purge cycle to regenerate the desiccant. Further, regenerating the desiccant in this type of air dryer depletes some of the stored, compressed air that could otherwise be used to operate the brakes. In addition, before air enters the cartridge to be treated by the desiccant, it must be cooled to a sufficient temperature, which is typically accomplished by routing the air through a long cooling line positioned between the air compressor and air dryer.
Another type of air dryer includes dual cartridges each including desiccant that dries compressed air. The air dryer includes an internal valve mechanism that controls air flow through the cartridges. When one cartridge dries air from the air compressor, air from the storage reservoir may be sent in reverse through the other cartridge to regenerate the desiccant. While this type of air dryer may continuously dry air, it depletes the stored, compressed air for regeneration of the desiccant like the single cartridge air dryer described above. Further, it also requires a long cooling line to cool air from the compressor before it enters the air dryer.